In France, between 450,000 and 600,000 people live in accommodation that is deemed not fit for purpose. The southern city of Marseille is particularly affected. Our reporters Julia Guggenheim and Jonathan Walsh met local residents, four years on from the tragedy in Marseille's central rue d'Aubagne, where eight people died after two buildings collapsed. We also speak to Kevin Vacher, an activist for decent housing in Marseille.